Drop incorrect constant names from test.

We don't generate these names any more.
Don't print non-variables as new arguments.

This screen real estate should only be taken up by newly-referenced variables, not constants or ANY values.
Add simple test for field assignment.

This test will need to be fleshed out when the field assignment instrumentation code is more complete.
Structure field annotation support.
Field assignment instrumentation.

Add instrumentation support for assignments to structure fields. These assignments can be simple (x.y = 42) or compound (x.y += 1 / x.y++), but mixing the two types is a bad idea, since they can alias.

TODO: add a warning when potentially-aliasing assignments are instrumented.